Not Applicable.
The present invention relates to the field of communication systems. More particularly, this invention comprises methods and apparatus for providing many individual customers with symmetric access to a broad-band, wide-area network, especially where capable telecommunications infrastructure is non-existent or very expensive to install.
In the past few years, a new information revolution has caused the demand for communications to skyrocket. The emergence of the Internet as a new distribution and business medium, coupled with the continuing improvements in computing speed and power, have strained the ability of conventional networks to meet this burgeoning demand.
The installed base of conventional copper wires present inherent limitations and constraints to providing enhanced levels of communications services. Although new compression and signal processing techniques have enabled telephone companies to offer faster speeds and greater bandwidth using new services such as ISDN, DSL and ADSL, the market demand for more capacity will soon outpace these recent innovations. The use of optical fiber and cable television networks for new modes of communication is increasing, but fibers and cables have their own drawbacks and are relatively expensive to install and to maintain. Several satellite systems, including Teledesic(trademark), Iridium(trademark) and Globalstar(trademark), are planning to offer world-wide high-speed services, but most of these companies will not roll out their full panoply of services for several years.
Each of these technologies supplies part of a solution to the problem of offering an improved global network, but none of them have yet conquered the holy grail of the telecommunications industry, the xe2x80x9clast milexe2x80x9d of service. The most expensive segment of furnishing service to a customer is usually the last mile of the connection to the customer""s location.
Several attempts to solve the problem of distributing information to large numbers of subscribers have met with mixed results. A number of these attempts are summarized below.
U.S. Pat. No. 2,288,802 issued to John Hays Hammond in 1942 and entitled Signaling System discloses a radio transmission system which employs a carrier wave that is transmitted in two substantially independent channels. The channels are xe2x80x9cmade independentxe2x80x9d by using polarizations which propagate at right angles to each other. The carrier waves may also be modulated xe2x80x9cby the same signal frequency, but with a predetermined phase relationship between the two modulations.xe2x80x9d See Hammond, Column 1, Lines 1-24.
U.S. Pat. No. 4,747,160, issued to Bernard Bossard on May 24, 1988 and entitled Low Power Multi-Function Cellular Television System describes a network of low power, substantially omni-directional cell node transmitters which communicate with a directional receiving antennas. Bossard""s omni-directional transmitter imposes severe constraints on the ability of this system to provide diverse information services to many different customers.
One particular disadvantage of Bossard""s system, which is due to its omni-directional signal, is the limitation of the system to compensate for rainfall in small portions of customer cells. Since the entire signal must be amplified at an omni-directional broadcast node, the system runs the risk of overpowering the signal to customers which are unaffected by the storm fronts. Bossard compensates for this constraint by limiting cell size.
Another severe limitation of the Bossard invention is the inability of the Bossard system to transmit to a single customer, or to transmit different signals to many different customers. The cell size in Bossard""s system is also limited to the amount of power generated, which is dependent on the available (TWT) of about 100 watts. The base case for Bossard""s system might be a quadratic cell for a xe2x80x9csubstantiallyxe2x80x9d omni-directional system, in which a 100 watt TWT might be located in each of four quadrants of a broadcast cell, limiting the cell broadcast power to approximately 400 watts.
In 1977, Xerox Corporation initiated work on the Xerox Telecommunications Network (XTEN), a nationwide, high-speed, end-to-end, digital communications service. XTEN was designed to provide local data services using a combination of substantially omni-directional transmission from cell nodes and point-to-point return links from transceivers located at business premises. Local networks were to be connected by intercity satellite or terrestrial xe2x80x9cbackbonexe2x80x9d facilities. See Xerox Petition for Rulemaking, filed with the Federal Communications Commission on Nov. 16, 1978. See also Xerox Comments on the DTS Notice of Proposed Rulemaking, filed with the Federal Communications Commission on Jan. 14, 1980.
Siemens Corporation received U.S. Pat. No. 1,586,260 from the Federal Republic of Germany in 1977. This patent, entitled A Radio Telecommunications System, discusses a system which connects stationary subscriber stations to a telecommunications network such as a public telephone network. A radio concentrator, assigned to a dial-operated exchange, is connected to the stationary subscribers via an omni-directional antenna. See Siemens ""260, Column 1, Lines 9-13 and Lines 21-24.
Siemens was also awarded French Patent No. 1,024,523 entitled Rxc3xa9seau d""xc3xa9metteurs d""ondes Ultra-courtes, which also pertains to transmission of radio and television programs. See Siemens ""523, Resumxc3xa9, Column 4.
In June of 1982, George Jacobs published a paper entitled Low Power Television in IEEE Spectrum. Jacobs explains the impact of the development of short-range, low-cost television systems. FIG. 3 of his article reveals the components of a low-power television station designed to produce electromagnetic power of a kilowatt or less.
Donald Silverman offers an analysis of an integrated, end-to-end digital communications service which may be used to augment existing inter-city network facilities in his paper entitled The Digital Termination System Solution for High Speed Local Distribution. This paper was published in the January, 1983 edition of Microwave Journal.
The IEEE Spectrum published a paper in June, 1983 by George Cooper and Ray Nettleton entitled Cellular Mobile Technology. The Great Multiplier. This article discusses the advantages of a cellular mobile communications system, interference problems, narrowband modulation, digital transmission, space diversity techniques which reduce fading and spread-spectrum and frequency hopping methods.
In their paper entitled Multiple Access Digital Microwave Radio System for Local Subscribers, Nasatoshi Murakami et al. describe a radio communication system which provides point-to-multipoint digital transmission in a metropolitan area. See IEEE International Conference on Communications ""83, June 1983, pp. b2.5.1.
In an article entitled Digital Termination Systems, Walter Urich and Ronald Bohm describe a common carrier service designed to provide flexible, low-cost digital communications within a community using a portion of the microwave spectrum. See Computerworld, Jun. 6, 1984, pages 35-38.
In U.S. Pat. No. 4,525,861 issued in 1985, Thomas Freeburg explains the details of his Zoned Data Communications System for Communicating Message Signals between Portable Radios and a Host Computer. This system serves a geographic area that is divided into a number of non-overlapping zones. Signals carrying alphanumeric information are conveyed among a general communications controller and a number of portable radios. See Freeburg, Abstract, Lines 1-9.
Douglas Morais describes a Radio Communication System Using Frequency Division Multiplexing for Transmission between a Master Station and a Plurality of Remote Stations in his U.S. Pat. No. 4,528,656, printed in 1985. Morais"" point-to-multipoint radio communication system includes a master station and a number of remote stations which communicate using frequency division multiplexing.
Alfred Mack discusses his Radio Communication System in his U.S. Pat. No. 4,633,463, granted in 1986. Mack""s invention pertains to tactical military applications, and includes at least one remote station associated with each of several central stations. Each central station is connected to an omni-directional antenna, while each remote station is connected to a directional antenna. Each central station transmits at a distinct frequency, and each remote station is tuned to receive only the one frequency which is transmitted by its associated central station. See Mack, Abstract, Lines 1-11.
Minoru Kawano was granted U.S. Pat. No. 4,704,733 for his Cell Enhancer for Cellular Radio Telephone System Having Diversity Function in 1987. His invention concerns a cell enhancer for use by one cellular provider in a cellular radio-telephone system. This cell enhancer has an xe2x80x9cup-streamxe2x80x9d antenna system directed at the cell site for receiving the transmitted down-link signal from the cell site. See Kawano, Abstract, Lines 1-10 and Column 2, Lines 38-42.
John R. Mihelich published a paper entitled Mitchell Commits to Cellular Television Study in the February, 1991 edition of Private Cable. Mihelich discusses the prospects for universal multi-channel cellular television service.
Siemens holds German Patent No. 2659638, which is entitled xe2x80x9cFunksystem zum Anschluxcex2ortsfester Teilnehmerstationen an ein Nachrichtennetz.
European Patent Application No. 86303185.2, by Acampora et al., describes a terrestrial radio system which utilizes spot beam time division multiple access and frequency re-use to provide communication services from a base station to remote customer within a system service region.
PCT Patent Application No. PCT/SE90/00681, by Ahl et al., describes a method and a communications system for local dynamically connectable digital synchronous multiplex service networks.
PCT Patent Application No. PCT/DE93/00382, by Ritter et al., describes a mobile radio network with central cell beaming.
U.S. Pat. No. 4,785,450, by Bolgiano et al., describes a communication system that comprises a plurality of subscriber stations in RF communication with a base station having multiple sequentially repetitive time slots.
In the article entitled New AUTOPLEX Cell Site Paves The Way For Digital Cellular Communications, Hardy and Lemp describe a cell site that has distributed rather than centralized control.
European Patent Application No. 85307456.5, by Horne, describes a cryptographic system for a direct broadcast satellite network.
Ascom Zelcom AG has filed European Patent Application No. 89117388.2, which is entitled Digitales Funkxc3xcbertragungssystem fxc3xcr ein aus Zellen aufgebautes Netz unter Verwendung der Bandspreiztechnik.
UK Patent Application No. GB 2 261 575 A, by Marsh et al., describes a method of establishing a telecommunications network between subscriber stations and their associated local station. The network is managed using a system controller.
The problem of overcoming the relatively high cost of offering high-speed and high-bandwidth services to many different kinds of customers over the xe2x80x9clast milexe2x80x9d of the global network has presented a major challenge to the telecommunications industry. The development of an intelligent and versatile local, multiple-point distribution system would constitute a major technological advance and would satisfy a long felt need in the telephone, entertainment and information businesses.
The present invention provides symmetric communications access to a wide area network (WAN) for a very large number of users who send information to and receive information from the network. The invention offers an inexpensive xe2x80x9clast-milexe2x80x9d hookup to a very large number of subscribers which can be implemented particularly where a high data-rate capable telecommunications infrastructure does not exist. The use of copper telephone wires, commonly called twisted pairs, to carry information signals is possible at low data rates, but at high data rates, these wires cannot carry information signals over much distance because of losses. Low loss conductors such as coaxial cable or optical fibers are expensive in themselves, and the cost of stringing or burying these cables to bring them to an individual subscriber is usually prohibitively expensive, particularly in densely settled urban communities.
One of the preferred embodiments of the Network Access Communication System combines features of a local area network (LAN) infrastructure with the high data-rate capabilities of microwave or millimeter wave transmissions from a subscriber terminal to a central communications hub. Distributed routing of the information signals provides subscribers with low latency (no-waiting) symmetric transmission of information signals at speeds of about ten million bits per second (10-Mbps). Availability of a communication path in this system approximates that of a fiber optic cable, from 99.7 to 99.9% of time. The system has a low bit error rate (approximately one bit in 10xe2x88x928 bits) and a high frequency re-use factor. Among the information exchange protocols the system supports is the transmission control protocol, Internet protocol (TCP/IP) suite.
One of the preferred embodiments of the Network Access Communication System comprises a plurality of service areas in which subscribers are located. Each service area has a communications hub which is connected to a wide area network such as the Internet. Each subscriber is connected to a subscriber terminal, either directly or through a local area network (LAN) serving many other subscribers. In one embodiment, the interface to the local area network operates full duplex on the Ethernet 10BaseT standard. The LAN may be operated by or through a local public switched telephone network (PSTN). Each subscriber terminal is coupled to a communications hub by a radio link operating at frequencies in the microwave or millimeter wave bands. A preferred frequency band is 59-64 GHz, but other bands from 3 GHz to 300 GHz can be used. At these frequencies subscriber terminal antennas are very small, about six inches diameter or less.
Each service area is divided into sectors. The number of sectors may vary depending on the density of subscribers. A sector can efficiently support approximately 200 subscribers. One to forty sectors per service area are preferred. One embodiment of the invention has a service area with eight sectors. An eight sector service area can therefore efficiently support approximately 1,600 subscribers. One or more subscribers generally will be connected to a local area network. Typically, the communications hub is centered in the service area. A service area may have a radius of approximately 0.7 to 1.5 kilometers (km), yielding a coverage area of 1.5 to 7 km. Service areas may be abutted or overlapped to cover larger included areas. Other arrangements are possible, including overlapping the service areas so that individual subscribers will be within line-of-sight of a communications hub. The arrangement of service areas can be readily adapted to the terrain, the existing infrastructure and the number of subscribers contemplated.
Packets of information are transported by the system from a subscriber and routed to a network service provider connected to the WAN. The router functions are distributed between the communications hub and one or more subscriber terminals. A multi-port router delivers the packets to and from the communications hub and the WAN. A two-port router delivers the packets to and from a subscriber terminal to connected subscribers using the LAN.
The communications hub comprises a network unit (NU) and a radio unit (RU). The radio unit has a transceiver and multiplexer/demultiplexer unit. The network unit contains a multi-port router which is coupled to a wide area network (WAN) port. The transceiver transmits to and receives signals from the subscriber terminals in the sectors of the service area. Atmospheric oxygen absorption of these signals is such that low-power, subscriber terminal transmitters, not requiring licenses by the Federal Communications Commission, can operate successfully over a distance of one to two kilometers, the radius of a service area. The multiplexer/demultiplexer unit receives and multiplexes subscriber message traffic onto 100BaseT ports and forwards this traffic to the multi-port router. The message traffic is then passed to the WAN port for transmission to a wide area network service provider, for example, an Internet service provider (ISP).
The subscribers and the subscriber terminal share a single LAN, for example, a 10BaseT Ethernet(trademark). The subscriber terminal comprises a transceiver and a two-ported router connected by a serial interface. The two-port router serves as the subscribers gateway to the network. Local subscriber-to-subscriber intranet communication takes place over the LAN. A subscriber communication to the wide area network proceeds to the subscriber terminal. The signals then pass through the two-port router, a transceiver and a radio link to the communications hub where they are processed as described above. Other routed or switched LAN structures are possible. In the simplest case, a single subscriber is connected directly to a subscriber terminal 10BaseT port. Individual residential subscribers having a single personal computer are most likely to be connected this way. Signals returning from the WAN follow the reverse path to the subscriber.
To avoid interference between subscribers and to provide very high speed information transfer to the large number of users contemplated, the radio communication link in one embodiment incorporates time division duplex (TDD), multi-frequency, time division multiple access (MF-TDMA), channel hopping, sixteen-frequency shift keying (16-FSK) modulation and concatenated coding features Other alternatives to TDD include frequency division duplex (FDD), code division duplex (CDD) and polarization division duplex (PDD). Other usable multiple access techniques include time division (TDMA), frequency division (FDMA), code division (CDMA), polarization division (PDMA), multi-frequency CDMA, multi-frequency PDMA and combinations ofthese. Modulation techniques include binary FSK, M-ary FSK, where M=3, 4 . . . 100, or more and M-ary versions of phase shift keying (PSK). Other usable modulation techniques include M-ary versions of amplitude shift keying (ASK), quadrature amplitude modulation (QAM), pulse position modulation (PPM), Gaussian minimum shift keying (GMSK), continuous phase frequency shift keying (CPFSK), vestigial sideband (VSB) and continuous phase modulation. As before, M=2, 3, 4 . . . 100, or more. Alternative coding schemes include block codes, convolutional codes, turbo codes, turbo block codes and combinations thereof.
In one embodiment, the 59 to 64 GHz radio frequency band is divided into twelve sub-bands of 416.7 MHz each. For communication hubs with from one to twelve sectors, each sector is assigned to a different frequency sub-band. For hubs with from twelve to twenty four sectors, the sub-bands are used up to two times per hub. For hubs with from 25 to 36 sectors, the sub-bands are used up to three times per hub, and for 37 to 48 sectors, they are used up to four times.
In one embodiment of system, which operates in a time division duplex (TDD) mode, a novel radio-frequency circuit is used which acts as a receiver front end or a transmitter final stage depending only on the switching of the signal path between components. It is an elegant solution to the implementation of a high-speed, symmetric-path, radio signal between a subscriber terminal and a WAN. Switching times of about one millisecond permit flow of information in either direction over the SHF radio links between subscriber terminals and communications hub. The circuit comprises an amplifier, a filter, a frequency mixer and four switches. The circuit can be operated at any frequency band from direct current (dc) to light. In the case of the instant invention, it is operated at SHF. When switched to operate as a receiver front end, the circuit performs a low-noise down conversion from radio frequency (RF) to an intermediate frequency (IF). When switched to operate as a transmitter final stage, the circuit performs an up-conversion from IF to RF and a final amplification.